This invention relates to a phase error corrector for an HDTV reception system, which can correct data level errors by reducing phase noise coming from local oscillators.
FIG. 1 is a general HDTV reception system proposed by the Grand Alliance.
As shown in FIG. 1, in general, the HDTV reception system includes a tuner 1 for converting a RF signal received through an antenna into an IF signal, an IF filter and synchronous detector 2 for converting the IF signal received from the tuner 1 into a baseband signal and detecting synchronism from the baseband signal, a synchronous and timing detector 4 for detecting various clock signals and control signals from the baseband signal received from the IF filter and synchronous detector 2, an NTSC removing filter 3 for removing NTSC signals from the baseband signal received from the IF filter and synchronous detector 2, an equalizer 5 for correcting distorted signals received from the NTSC removing filter 3, a phase error corrector 6 for removing phase errors formed by local oscillators from the signals received from the equalizer 5, a slicer 7 for slicing the signals received from the phase error corrector 6 to obtain an original data level, a data deinterleaver 8 for deinterleaving the data received from the slicer 7, a Reed-Solomon decoder 9 for Reed-Solomon decoding of the data received from the data deinterleaver 8 for correcting errors, and a data de-randomizer 10 for de-randomizing the data received from the Reed-Solomon decoder 9 for restoring the signals de-randomized at a transmission side.
Herein, in general, the phase error corrector 6 removes phase errors mostly formed by a local oscillator used in the tuner 1, of which phase error is to be explained hereinafter in detail, referring to FIGS. 2 and 3.
FIG. 2 shows an 8 VSB(Vestigial Side Band) constellation, wherein the I value is actual data, and the Q value is, not discrete, but continuous, and varies depending on the I value.
In FIGS. 2 and 3, the reason that each of the horizontal lines of the I value has a certain thickness is due to white noise.
The 8 VSB constellation of FIG. 2 is distorted into a constellation as shown in FIG. 3 due to phase errors caused by local oscillators.
That is, as shown in FIG. 3, the phase errors, i.e., the errors due to phase noise projected normal to I axis becomes greater for the same I value as the Q value becomes greater, which is to be explained hereinafter, referring to FIG. 4.
FIG. 4 is an enlargement of K part of FIG. 3 showing data level errors caused by phase noise.
For example, in case an original data position is "0", and if the data position is moved to "0'" due to a phase error, although the I value of the original "0" projected normal to I axis is "A" an actual I value of the original "0" projected normal to I axis moves to "A'" due to the phase error. Therefore, the I axis component error "A" from "A'" which causes a data level error when it is sliced at the slicer 7, causes a slice error. Herein, an angle between the original data position "0" and actual data position "0'" by the phase error is a phase error caused by phase noise.